It is well known to use switch units as building blocks of higher capacity switches using cascaded multi-stage structures. If the switch units in a time-multiplexed multi-stage switch have buffers, a path through a multi-stage switch is established as a number of decoupled simple switching processes which greatly simplify connection setup in a multi-stage switch. With bufferless switch units, such as optical switch units, finding a path through a time-multiplexed multi-stage switch involves a processing-intensive connection setup.
A mesh structure of switch units, whether using buffered or bufferless switch units, may be preferable to an unfolded cascaded multi-stage structure because a proportion of connections may be routed through paths traversing fewer switch units in comparison with cascaded structures.
Fast optical switch units, suitable for use in a time-shared switching node, are limited to small dimensions; e.g., 64×64. A first-order mesh of 64×64 switch units can produce a switch of approximately 1000 dual input/output ports. A second order mesh using switch units each of dimension 64×64 can produce a switch of more than 10000 dual ports. However, connectivity for a second-order mesh of bufferless switch units employed in a fast-switching time-shared network is generally determined using a fourth-order time-slot-matching process for a significant proportion of connections. This complicates the scheduling process and may lead to low utilization of the switch fabric.
Future networks are likely to use fast optical switches in the core, and core switches are required to be of large dimension in order to reduce the mean number of hops and, hence, improve network performance and reduce cost.